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Soil testing is a valuable part of blueberry nutrition programs. Soil pH needs to be monitored routinely because pH influences the availability of many nutrients to plants. Blueberries require relatively small amounts of most nutrients. Most soils can supply adequate quantities if the pH is maintained in the proper range.
Soil tests also provide estimates of the quantities of other nutrients. Soil tests provide rough estimates of nutrient availability to plants. Leaf analysis provides a means of accurately identifying nutritional problems that are difficult to diagnose by soil testing or by observing the appearance of the bushes.
Soil samples should be collected one to two years before planting blueberries to determine if the soil pH is in the proper range. This allows adequate time to apply the acidifying material or limestone and for it to adjust the soil pH.
Soil pH or nutrient levels can vary greatly over short distances. Collect enough soil samples to adequately represent the proposed planting site. As a general rule, collect at least one sample from each 10- to 12-acre area on uniform sites with little visible variation of soil characteristics.
If the soil organic matter, soil texture or previous crop history varies significantly, collect a separate sample from each distinctly different area. It might be necessary to collect samples from 2- to 3-acre areas to properly characterize a highly variable site.
Each soil sample should be a composite of 20 to 30 subsamples (cores) taken from throughout the sampling area, then mixed thoroughly. The soil sample should be properly identified with necessary information including location and depth.
Blueberries may root to depths of 12 to 15 inches. Collecting only a shallow sample may give misleading information if the soil pH or nutrient levels vary with depth. Collecting a separate topsoil sample (from 0 to 8 in for soil pH and nutrient analysis) and a subsoil sample (from 8 to 16 in for soil pH) will provide a better understanding of the soil variability.
Adjust the pH of blueberry soils, if needed. Blueberries may perform well when soil pH is between 4.0 and 5.5, but a soil pH of 4.5 to 5.0 appears to be best. Apply lime if the pH is below 4.0.
If soil pH is greater than 5.5, apply adequate elemental sulfur to decrease pH to 4.5. The amount of sulfur required is very dependent on soil texture. Ferrous sulfate and aluminum sulfate are also used to lower soil pH, but they are more costly to use than sulfur.
Sandy soils require comparatively small amounts of sulfur to reduce the soil pH. Adjusting the soil pH requires higher rates of sulfur if soils have a high clay content or high organic matter level.
It is important to apply and incorporate the sulfur at least one year before planting to allow the sulfur time to react and adjust the soil pH. If large changes in pH are needed, check the soil pH again just before planting and apply additional sulfur if needed.
Sulfur cannot be incorporated into the soil to change the pH quickly after the bushes have been planted. Do not apply more than 250 to 350 pounds of sulfur per acre to established blueberry plantings at one time. When large amounts of sulfur are needed are needed, spread the application out over several years.
The blueberry plantings should be sampled at least every three to four years. All of the blueberry plantings may be sampled the same year or portions may be sampled more frequently on a rotating basis. Sample at any convenient time of year.
Collect soil from within the row to a depth of 8 inches. Soil sampling is particularly important where the soils have been acidified. If the acidifying material was applied to the soil surface and not incorporated, the soil pH will likely increase with depth.
Collecting separate topsoil and subsoil samples (0 to 8 inches and 8 to 16 inches) for pH analysis will identify whether the soil has been acidified adequately. Acidified soils often increase in pH over time, so these plantings need to be monitored more frequently than sites on naturally acidic soils.
Adapted from Hanson & Hancock. 1996. Managing the nutrition of Highbush blueberries. Ext. Bull E-2011. Michigan State University Extension, East Lansing, Michigan